The invention relates to controllers for internal combustion engines.
FIG. 6 is a diagram showing a construction of an exemplary fault judging system in a conventional controller for an internal combustion engine. In FIG. 6, reference numeral 1 designates an engine; 2a, a surge tank disposed on an intake manifold 2 of the engine 1; 3, a throttle valve; 4, an EGR valve; 5, an EGR control solenoid; 6, a pressure sensor for measuring pressure within the surge tank 2a; 7, a canister for absorbing transpired fuel gas produced within a fuel tank (not shown); 8, a purge air introducing path extending from the canister 7 and connected to the surge tank 2a; 9, a purge control solenoid disposed within the purge air introducing path 8 and serving as a control valve to cause the engine 1 to suck the purge air under predetermined operating conditions; and 10, an engine control unit (ECU).
FIGS. 7 and 8 are time charts showing exemplary operations of fault judging systems employed in the conventional internal combustion engine controller. FIG. 7 shows an operation of a purge fault detecting system monitor; and FIG. 8 shows an operation of an EGR fault detecting system monitor.
In FIG. 7, "Purge" indicates an operating condition of the purge control solenoid 9; and "F/B I" indicates an integrating coefficient in a feedback control of an air-to-fuel ratio of the fuel supply system. In FIG. 8, "EGR" indicates an operating condition of the EGR valve 4; and "P" indicates pressure detected by the pressure sensor 6.
The principle of fault judgment will be described with reference to FIGS. 6 to 8. In the purge fault detecting system monitor, a mean value Im1 of the integrating coefficient in the air-to-fuel ratio feedback control of the fuel supply system with the purge control solenoid 9 closed and a mean value Im2 thereof with the purge control solenoid 9 open are obtained. If the absolute value of their difference (.vertline.Im1-Im2.vertline.) is smaller than a predetermined value, then the purge fault detecting system is judged abnormal. As a result of the judgment, abnormalities such as defective operation of the purge control solenoid 9, wire breakage, leakage of the piping system, or the like are located. Conversely, if the absolute value is greater than the predetermined value, the purge fault detecting system is judged normal.
In the EGR fault detecting system monitor, a pressure Pe1 and a pressure Pe2 within the surge tank 2a respectively measured by the pressure sensor 6 under the conditions that the EGR valve 4 is closed and that the EGR valve 4 is open with the purge control solenoid 9 closed are obtained. If their difference (Pe2-Pe1) is smaller than a predetermined value, then the EGR fault detecting system is judged abnormal. As a result of the judgment, abnormalities such as defective operation of the EGR valve 4, wire breakage, leakage of the piping system, or the like are located. Conversely, if the absolute value is greater than the predetermined value, the EGR fault detecting system is judged normal.
The conventional internal combustion engine controller of this type is designed to measure pressure change by the pressure sensor 6 using a pressure pipe 11 as shown in FIG. 6. Affected by dust and moisture contained in an EGR gas, foreign matter adheres to or gets frozen at the pressure sensor 6 and the pressure pipe 11 to clog them, which is a problem encountered by the conventional controller.
Further, in the purge fault detecting system monitor of the fault judging system, the air-to-fuel ratio of the mixture of fuel and air sucked into the engine 1 by introducing the purge air is changed toward the lean side or toward the rich side if the fuel adsorbing rate within the canister 7 is either 0% or 100%, so that normal/abnormal judgments based on the above-mentioned principle can be achieved. However, if the fuel adsorbing rate is an intermediate value, then change in the air-to-fuel ratio of the mixture of fuel and air is so small even at the time of introducing the purge air that the normal operation can erroneously be judged as abnormal, which is another problem.
Still further, if the purge system fault detection is based on the difference in pressure, then another pressure sensor must be provided.
Still further, no flow rate limiting means is disposed along the introducing path. Therefore, the advantage that deviation in pressure is increased at the location of such means cannot be obtained, thereby not improving the performance of the pressure sensor 6.